The well defined biology of the lower eucaryote Physarum polycephalum will be used to study the biochemistry and possible translational and nontranslational regulatory roles of tRNA throughout growth and differentiation and during the transition between these two life cycle phases. Studies are divided into 3 areas: 1) determination of nucleotide sequences and codon responses for four apparently unique growth phase tRNAs; 2) quantitative and qualitative studies of the 20 tRNA families throughout differentiation using acylation levels and RPC chromatography and comparison of the data with those already obtained during growth. This work will also include comparisons of the ability of growth phase synthetases to acylate differentiation phase tRNAs and vice versa; 3) any quantitative or qualitative differences noted, particularly the expected quantitative ones, will be further studied with reference to the mechanism of the change. To that end, both rates of synthesis and rates of turnover will be established for the individual tRNA isoacceptors of interest after P32 or H3 methyl methionine labeling and subsequent purification of specific tRNA families by phenoxyacetylation and BD-cellulose chromatography.